Update links extend -> ninenines

doc/src/guide/getting_started.ezdoc

@@ -14,7 +14,7 @@ you need to push your first Cowboy application to production.
 
 :: Bootstrap
 
-We are going to use the ^"erlang.mk^https://github.com/extend/erlang.mk
+We are going to use the ^"erlang.mk^https://github.com/ninenines/erlang.mk
 build system. It also offers bootstrap features allowing us to
 quickly get started without having to deal with minute details.
 
@@ -29,7 +29,7 @@ Then we need to download `erlang.mk`. Either use the following
 command or download it manually.
 
 ``` bash
-$ wget https://raw.githubusercontent.com/extend/erlang.mk/master/erlang.mk
+$ wget https://raw.githubusercontent.com/ninenines/erlang.mk/master/erlang.mk
 ```
 
 We can now bootstrap our application. Since we are going to generate

erlang.mk

@@ -93,7 +93,7 @@ export ERL_LIBS
 PKG_FILE2 ?= $(CURDIR)/.erlang.mk.packages.v2
 export PKG_FILE2
 
-PKG_FILE_URL ?= https://raw.githubusercontent.com/extend/erlang.mk/master/packages.v2.tsv
+PKG_FILE_URL ?= https://raw.githubusercontent.com/ninenines/erlang.mk/master/packages.v2.tsv
 
 # Core targets.
 

rebar.config

@@ -1,4 +1,4 @@
 {deps, [
-	{cowlib, ".*", {git, "git://github.com/extend/cowlib.git", "1.0.0"}},
-	{ranch, ".*", {git, "git://github.com/extend/ranch.git", "1.0.0"}}
+	{cowlib, ".*", {git, "git://github.com/ninenines/cowlib.git", "1.0.0"}},
+	{ranch, ".*", {git, "git://github.com/ninenines/ranch.git", "1.0.0"}}
 ]}.